Donald Trump has been fueled to the Republican presidential nomination by "taking what talk radio has been talking about for 20 years and expanding on it and taking it to the presidential level," political commentator Michael Reagan said Thursday.

"What you see behind him is those programs," the eldest son of former President Ronald Reagan told Don Lemon on CNN. "The people that talk to him, the people that support him, are people who have been listening to talk radio for the last 20 years.

"They have a hero now in him," Reagan said.

Trump Thursday secured the 1,237 delegates he needed to win the nomination after North Dakota Republicans awarded him its 28 unbound delegates. The Peace Garden State did not hold a primary or caucus.

Donald Trump has been fueled to the Republican presidential nomination by "taking what talk radio has been talking about for 20 years and expanding on it and taking it to the presidential level," political commentator Michael Reagan said Thursday.